Over its past four years, the Program Project has made ever-increasing use of sophisticated genetic strategies for probing gene function. A key component of the portfolio is a genome-wide RNAi resource that can be used to probe the function of individual genes or to carry out genome-wide searches for those loci that impact a process of interest. The core not only manages the Program's large-scale RNAi libraries but provides all necessary support for their use. The eight major functions of this core are as follows. 1. Curation of large scale shRNA vector libraries 2. Distribution of individual clones and clone sets to Program members 3. Design of RNA-based inhibitors 4. Quality control of RNAi tools 5. Construction of custom RNAi vectors 6. Support production of recombinant retroviruses 7. Quality control of tissue culture reagents 8. Archiving and distribution of reagents to the community Through these services, the Core provides support to every Project within this Program and also plays an essential role in making the RNAi reagents developed at CSHL available to the broader scientific community. This Core provides the only grant support for the management of the genome-wide RNAi libraries that have been widely disseminated directly through the work of this Program.